Xeon E5 processors with 4, 6, 8, and 12 cores. Be smart in choosing. If your key apps don't use all 12 cores, consider a model with lesser cores but with higher core frequency.

Faster memory bus (60GB/s) with 1866MHz modules, but only four memory slots limit you to 64G (16G x 4). We are running 96G in a 2010 Mac Pro 12 core tower.

Dual AMD FirePro GPUs on a faster PCIe 3.0 bus. Of the three models, the top D700 is on par with Radeon R7970 we tested but with more VRAM per card. Excellent OpenCL acceleration but until pro app developers get off their "CUDA only" kick, GPU acceleration will be lacking for apps like OctaneRender and After Effects ray-traced 3D.

Supports up to three 4K displays. Too bad Apple doesn't make 4K displays. The 4K displays available from third parties are u-g-l-y plastic 'ducks.'

Up to 1TB internal Flash storage is faster than PCIe flash in other 2013 Macs (1200MB/s vs 780MB/s). If you need more storage, you must purchase external USB 3.0 or TB enclosures or use a TB expansion chassis for existing SAS/SATA host adapters. Messy, noisy desk top clutter.

Thunderbolt 2.0 is twice as fast as Thunderbolt 1.0. Plus the Mac Pro sports three channels with two ports each. (Other Macs with TB are single channel, two ports.)

Quiet at 12 dB (though peripherals with fans will raise the dB level on your desk).